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Units of Radiation Measurements, Quality
Specification, Half-Value Thickness, Filters, and
Filtration
Presenter: Dheeraj Kumar
MRIT, Ph.D. (Radiology and Imaging)
Assistant Professor
Medical Radiology and Imaging Technology
School of Health Sciences, CSJM University, Kanpur
Basics of Radiation Measurements
Radiation measurements are essential for quantifying radiation
exposure, absorbed dose, and activity, providing crucial information for
medical physics and radiology. Let's delve deeper into the units and
their significance:
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
2
Gray (Gy)
• Definition: One gray is equivalent to the absorption of one joule of
radiation energy per kilogram of matter.
• Example: If a tissue absorbs 2 joules of radiation energy per kilogram,
the absorbed dose would be 2 Gy.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
3
Sievert (Sv)
• Definition: Sievert is a unit used to measure the biological effects of
ionizing radiation on human tissue.
• Conversion: 1 Sv = 100 rem (roentgen equivalent in man).
• Example: If an individual receives a dose of 0.1 Sv, it implies a
significant risk of developing radiation-induced cancer.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
4
Exposure Unit (Roentgen)
• The Roentgen (R) is a unit of measurement for ionizing radiation exposure, particularly in air. It quantifies the
amount of ionization produced by X-rays or gamma rays in a specific volume of air. The Roentgen is crucial
in radiation dosimetry and radiological safety. Let’s discuss into the theory of the Roentgen unit along with
examples:
Definition of Roentgen (R):
• The Roentgen is defined as the amount of X-ray or gamma radiation that produces one electrostatic unit of
charge (either positive or negative) per cubic centimeter of air under standard conditions of temperature and
pressure.
• The symbol for the Roentgen unit is "R."
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
5
Measurement of Radiation Exposure
Radiation exposure is measured by instruments called ionization chambers, which detect the ionization of air
molecules caused by incoming X-rays or gamma rays.
When radiation interacts with air molecules, it liberates electrons, resulting in ion pairs (positive ions and free
electrons).
The ionization chamber measures the total charge produced by these ion pairs, which is directly proportional to
the radiation exposure.
Calculation and Examples:
• One Roentgen (R) is equivalent to the generation of 2.58 × 10^−4 coulombs of charge per kilogram of air.
• For example, if a certain X-ray beam produces an exposure of 100 R, it means that the radiation has caused the
liberation of 2.58 × 10^−4 coulombs of charge per kilogram of air.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
6
4. Applications
The Roentgen unit is commonly used in various applications, including:
• Diagnostic radiology: To measure the intensity of X-ray beams used in
medical imaging procedures such as radiography and fluoroscopy.
• Radiation safety: To assess occupational and environmental exposure to
ionizing radiation and ensure compliance with safety regulations.
• Radiation therapy: To monitor and control the dose of radiation delivered to
cancerous tissues during radiotherapy treatments.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
7
Becquerel (Bq)
• The SI unit of radioactivity is the becquerel (Bq), named after Henri
Becquerel, the physicist who discovered radioactivity. The becquerel
is defined as one disintegration or radioactive decay event per second.
It quantifies the activity of a radioactive substance, representing the
rate at which its unstable atomic nuclei undergo radioactive decay.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
8
Measurement of Radioactivity
1 becquerel (Bq) = 1 disintegration/second
• Radioactivity is typically measured using specialized instruments such as Geiger-
Muller counters, scintillation detectors, or proportional counters.
• These instruments detect the ionizing radiation emitted by radioactive decay and
convert it into electrical signals or light pulses.
• The number of disintegrations detected per unit time provides the activity of the
radioactive substance in becquerels.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
9
Applications of the Becquerel Unit
1. Nuclear Medicine:
1. In medical imaging and therapy, radioisotopes are used as tracers or therapeutic agents.
2. The activity of radiopharmaceuticals is measured in becquerels to ensure the proper dosage for diagnostic or therapeutic
procedures.
2. Environmental Monitoring:
1. In environmental science, the concentration of radioactive isotopes in air, water, soil, and food samples is measured to assess
radioactive contamination.
2. Monitoring stations use becquerels to quantify the levels of radioactivity in the environment and to ensure public safety.
3. Industrial Applications:
1. In nuclear power generation, industrial processes, and non-destructive testing, radioisotopes are used for various applications.
2. The activity of radioactive materials in industrial processes is measured in becquerels to ensure safety and regulatory
compliance.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
10
REM
The REM (Roentgen Equivalent Man) is a unit of dose equivalent, used to quantify the biological effect of
ionizing radiation on human tissue. It takes into account both the absorbed dose of radiation and the relative
biological effectiveness (RBE) of the type of radiation. The REM unit is crucial in radiation protection,
occupational safety, and assessing the health risks associated with exposure to ionizing radiation.
• Definition of REM:
• The REM unit represents the dose equivalent in terms of the biological effect of ionizing radiation on human
tissue.
• It is defined as the product of the absorbed dose (measured in gray or rad) and a quality factor (dimensionless),
which accounts for the type of radiation and its relative biological effectiveness.
• 1 REM is equivalent to 0.01 sievert (Sv).
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
11
Calculation of REM
The formula to calculate REM is:
REM=Absorbed Dose (in rad or Gy)×Quality Factor (dimensionless)
• The quality factor depends on the type of radiation and ranges from 1 for low linear energy transfer (LET) radiation (such as X-rays
and gamma rays) to higher values for higher LET radiation (such as alpha particles and neutrons).
Examples of Quality Factors:
• X-rays, gamma rays, and beta particles: Quality factor = 1
• Alpha particles: Quality factor = 20
• Neutrons: Quality factor varies depending on energy and circumstances, ranging from 2 to 20 or higher
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
12
Applications of REM
1. Radiation Protection:
1. The REM unit is used in radiation protection guidelines and regulations to establish dose limits for occupational exposure to ionizing radiation.
2. Occupational dose limits are typically expressed in units of millirem (mrem) or REM.
2. Medical Dosimetry:
1. In medical radiation therapy, the REM unit is used to assess the potential biological effects of therapeutic doses of ionizing radiation on healthy
tissues and organs surrounding the targeted tumor.
3. Risk Assessment:
1. The REM unit plays a crucial role in assessing the health risks associated with radiation exposure and determining the appropriate safety measures
and protective actions to mitigate those risks.
1 REM = 0.01 Sv (sievert)
1 millirem (mrem) = 0.001 REM
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
13
Example
A radiation source emits radiation with an intensity of 10 mGy per hour at a distance of 1 meter. Calculate the absorbed dose at this distance.
Solution:
• The absorbed dose (D) can be calculated using the formula:
D= Intensity × Time
Given:
Intensity = 10 mGy/hour, Time = 1 hour
• Substitute the values into the formula:
D= 10mGy/hour × 1hour =10mGy
Therefore, the absorbed dose at a distance of 1 meter is 10 milligray.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
14
Quality Specification in Radiology
• Quality specification in radiology encompasses various parameters
that ensure optimal performance and safety.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
15
Image Resolution
• Definition: Image resolution refers to
the clarity or sharpness of an image,
determined by the number of pixels or
lines per unit length.
• Example: In digital radiography, a
higher resolution image allows for
better visualization of fine anatomical
structures, aiding in accurate diagnosis.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
16
Image Contrast
• Definition: Image contrast is the difference
in brightness or density between adjacent
areas on an image.
• Example: Contrast is crucial in
distinguishing between different tissues or
pathological conditions. For instance, in
mammography, a high contrast image
helps detect subtle abnormalities in breast
tissue.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
17
Image Noise
• Definition: Image noise refers to random
fluctuations in pixel values, resulting in a
grainy or speckled appearance.
• Example: Noise reduction techniques are
essential in computed tomography (CT) to
improve image quality. High noise levels
can obscure important details and
compromise diagnostic accuracy.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
18
Dose Optimization
Definition: Dose optimization aims to
minimize radiation exposure to patients while
maintaining diagnostic image quality.
Example: Utilizing dose-reduction techniques
such as automatic exposure control (AEC) in
radiography ensures that patients receive the
lowest possible dose without compromising
image quality.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
19
Compliance with Standards
Definition: Compliance with regulatory standards such as IEC 61223-3-
5 ensures adherence to specific quality assurance protocols.
Example: Regular quality control checks, calibration of equipment, and
documentation of procedures are essential for compliance with
standards, guaranteeing consistent and safe radiological practices.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
20
Half-Value Thickness (HVT)
Half-Value Thickness (HVT) is a fundamental
concept in radiation physics, particularly in
shielding design and radiation protection. Let's
delve deeper into HVT with numerical examples:
Definition:
1. HVT is the thickness of a material required to reduce
the intensity of a radiation beam by half.
2. It varies with the type and energy of radiation and the
material through which it passes.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
21
1. Radiation Attenuation:
When a radiation beam passes through a material, it interacts with the atoms in the material,
resulting in attenuation or reduction in its intensity.
• Attenuation can occur through processes such as absorption, scattering, and transmission.
2. Half-Value Thickness (HVT):
HVT is defined as the thickness of a material that reduces the intensity of a radiation beam
to half of its original value.
• It serves as a measure of the effectiveness of a shielding material in attenuating radiation.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
22
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
23
3. Factors Affecting HVT
The HVT of a material depends on several factors, including:
• Type of radiation: Different types of radiation (e.g., gamma, X-ray, neutron) have
varying penetration depths and require different thicknesses of shielding material.
• Energy of radiation: Higher energy radiation typically requires thicker shielding for
attenuation.
• Atomic number (Z) and density of the material: Materials with higher atomic
numbers and densities are more effective in attenuating radiation and may have
smaller HVT values.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
24
4. Applications and Examples
Medical Radiology: - In diagnostic radiology, lead aprons are
commonly used to shield patients from scattered radiation during X-ray
procedures.
Example: The HVT of lead for diagnostic X-rays may range from a few
millimeters to several centimeters, depending on the energy of the X-
rays and the required level of attenuation.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
25
Industrial Radiography: - In industrial radiography, lead or concrete
shielding is used to protect workers from exposure to radiation during
non-destructive testing.
Example: The HVT of concrete for gamma radiation used in industrial
radiography may be several centimeters, ensuring adequate protection
for workers in the vicinity.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
26
Nuclear Engineering: - In nuclear power plants, shielding materials
such as steel and concrete are employed to minimize radiation exposure
to personnel and the surrounding environment.
Example: The HVT of steel for neutron radiation in nuclear reactors
may be significant, requiring thick shielding to prevent radiation
leakage.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
27
5. Measurement and Calculation
• HVT can be determined experimentally by measuring the intensity of
radiation before and after passing through various thicknesses of
shielding material.
• Calculation of HVT involves logarithmic functions and is based on the
relationship between intensity and thickness of the shielding material.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
28
Example
Initial intensity of a gamma radiation beam: I0=100 mR/hourI0​=100mR/hour, HVT of lead for this radiation:
HVT Lead = 0.5 cm HVT Lead​ = 0.5cm
The formula to calculate the intensity after passing through a thickness of material is given by:
I=I0×0.5n
Where:
I = Final intensity after passing through thickness
n = Number of HVTs of the material
In this case, we want to find the intensity after passing through 1 cm of lead (which is twice the HVT):
n = ​​
Thickness of lead
𝐻𝑉𝑇 𝐿𝑒𝑎𝑑
=
1𝐶𝑚
0.5 𝑐𝑚
= 2 cm
Substitute n = 2 into the formula:
I =100mR/hour × 0.52 =100mR/hour×0.25 = 25mR/hour
Interpretation:
This means that after passing through 1 cm of lead, the intensity of the gamma radiation beam reduces to 25 mR/hour.
Such calculations are vital for designing effective radiation shielding in medical facilities, ensuring the safety of patients
and staff.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
29
Filters in Radiology
Filters play a crucial role in radiology by
modifying the quality and energy
spectrum of X-ray beams. Their function
and selection is essential for achieving
optimal image quality while minimizing
patient dose. Let's explore this topic in
detail, including common filter materials
and their effects on the X-ray spectrum:
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
30
Purpose of Filters
• Filters are employed in radiology to alter the energy distribution of X-
ray beams, thereby optimizing image quality and reducing patient
dose.
• By selectively filtering out low-energy photons, filters help enhance
image contrast and reduce scattered radiation, resulting in clearer
diagnostic images.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
31
Common Filter Materials
• Aluminum (Al): Aluminum filters are commonly used in X-ray equipment for general
radiography. They effectively remove low-energy photons from the X-ray beam, improving image
quality and reducing patient dose.
• Copper (Cu): Copper filters are utilized in mammography to enhance the visualization of breast
tissue. They selectively attenuate low-energy X-rays, allowing for better contrast and detection of
subtle abnormalities.
• Molybdenum (Mo): Molybdenum filters are specifically designed for mammography applications.
They help optimize the energy spectrum of X-rays, improving the visibility of microcalcifications
and small lesions in breast tissue.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
32
Effects of Filters on X-ray Spectrum
• Filters preferentially absorb lower-energy X-rays, resulting in a "hardening"
of the X-ray spectrum.
• As a result, the average energy of the X-ray beam increases, leading to
greater penetration of tissues and improved contrast resolution.
• Additionally, filters reduce the amount of low-energy radiation reaching the
patient's skin, thereby lowering skin dose and minimizing radiation risks.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
33
Importance of Filtration
Filtration is a critical aspect of radiology
that significantly influences image
quality, patient safety, and radiation dose
management. The importance of
filtration is essential for radiographers,
radiologists, and other healthcare
professionals involved in diagnostic
imaging.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
34
Enhancement of Image Quality
• Filtration helps improve image quality by selectively attenuating low-
energy photons, which are more likely to be absorbed by the patient's
body tissues and contribute to image noise.
• By removing these low-energy photons, filtration reduces scatter
radiation and enhances image contrast, allowing for better
visualization of anatomical structures and pathological findings.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
35
Reduction of Patient Dose
• One of the primary objectives of filtration is to minimize patient radiation dose
while maintaining diagnostic image quality.
• By filtering out low-energy radiation that contributes minimally to image
formation, filtration helps reduce unnecessary radiation exposure to the patient's
skin and underlying tissues.
• This is particularly important in pediatric imaging and for patients undergoing
repeated X-ray examinations, where dose optimization is critical for long-term
radiation safety.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
36
Compliance with Regulatory Standards
• Regulatory bodies such as the Food and Drug Administration (FDA) and the International Electrotechnical
Commission (IEC) establish guidelines and standards for filtration requirements in diagnostic X-ray equipment.
• Compliance with these standards ensures that imaging systems meet minimum filtration specifications,
guaranteeing consistent and safe radiation output.
• Regular quality control checks and documentation of filtration parameters are essential components of quality
assurance programs in radiology departments.
• Filtration plays a crucial role in reducing scatter radiation, which can degrade image quality and increase patient
dose.
• By attenuating low-energy photons that contribute to scatter, filters help improve the signal-to-noise ratio in X-ray
images, resulting in clearer and diagnostically relevant images.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
37
Types of Filtration
• In radiology, various types of filtration are employed to tailor the
energy spectrum of X-ray beams, optimize image quality, and
minimize patient radiation dose. The different types of filtration and
their applications is essential for radiographers, radiologists, and other
healthcare professionals involved in diagnostic imaging.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
38
Inherent Filtration
Definition: Inherent filtration refers to the filtration that
naturally occurs as X-rays pass through the components of
the X-ray tube and the surrounding materials before reaching
the patient.
Components: Inherent filtration includes the glass envelope
of the X-ray tube, the oil surrounding the X-ray tube, and any
additional filtration within the X-ray tube housing.
Purpose: The primary purpose of inherent filtration is to
remove low-energy, soft X-rays generated by the X-ray tube,
thereby ensuring that the X-ray beam has sufficient energy to
penetrate the patient's body and produce diagnostic images.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
39
Added Filtration
Definition: Added filtration involves the placement of
additional filters between the X-ray tube and the patient to
further modify the energy spectrum of the X-ray beam.
Materials: Common materials used for added filtration include
aluminum, copper, and rare-earth metals such as gadolinium.
Purpose: Added filtration helps attenuate low-energy X-rays
that are not useful for diagnostic purposes and contribute
primarily to patient dose and image noise. By removing these
low-energy photons, added filtration enhances image quality
and reduces radiation exposure to the patient.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
40
Total Filtration
Definition: Total filtration is the sum of inherent filtration
and added filtration.
Calculation: Total filtration is calculated by adding the
filtration contributed by the components of the X-ray tube
(inherent filtration) to the filtration provided by any
additional filters (added filtration).
Significance: Total filtration determines the overall quality
of the X-ray beam in terms of its energy distribution and
penetration characteristics. It is a crucial parameter for
ensuring compliance with regulatory standards and
optimizing radiation safety in diagnostic imaging.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
41
Example: Where we have an X-ray machine with inherent filtration of 0.5 mm aluminum equivalent and an additional aluminum
filter of 2.0 mm thickness placed between the X-ray tube and the patient. We want to calculate the total filtration provided by the X-
ray machine.
Inherent Filtration:
Inherent filtration refers to the filtration naturally present within the X-ray tube.
Given inherent filtration: 0.5 mm aluminum equivalent.
Added Filtration:
Added filtration consists of additional filters placed between the X-ray tube and the patient.
Given added filtration: 2.0 mm aluminum.
Total Filtration:
Total filtration = Inherent filtration + Added filtration
= 0.5 mm aluminum equivalent + 2.0 mm aluminum
= 0.5 mm + 2.0 mm
= 2.5 mm aluminum equivalent.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
42
Compensating Filtration
Definition: Compensating filtration involves the
use of filters that vary in thickness across the X-
ray beam to compensate for variations in tissue
thickness and density within the patient's body.
Applications: Compensating filters are
commonly used in mammography and dental
radiography to achieve uniform image density
and contrast across the entire image, even in
regions with varying tissue thicknesses.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
43
References
1. Bushberg, J. T., Seibert, J. A., Leidholdt Jr, E. M., & Boone, J. M. (2011). The Essential Physics of Medical Imaging. Lippincott
Williams & Wilkins.
2. Rehani, M. M., & Szczykutowicz, T. P. (Eds.). (2012). Radiation Dose Management in the Nuclear Industry: An Integrated
Approach. Springer Science & Business Media.
3. The International Electrotechnical Commission. (2017). IEC 61223-3-5: Medical electrical equipment - Characteristics of digital X-
ray imaging devices - Part 3-5: Determination of the detective quantum efficiency - Detectors used in mammography. IEC.
4. Shrader, J. A., Casarella, W. J., & Ritenour, E. R. (2016). Introduction to Health Physics. CRC Press.
5. Valentin, J. (2007). Radiation and Your Patient: A Guide for Medical Practitioners. International Atomic Energy Agency.
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
44

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Units of Radiation Measurements, Quality Specification, Half-Value Thickness, Filters, and Filtration.pptx

  • 1. Units of Radiation Measurements, Quality Specification, Half-Value Thickness, Filters, and Filtration Presenter: Dheeraj Kumar MRIT, Ph.D. (Radiology and Imaging) Assistant Professor Medical Radiology and Imaging Technology School of Health Sciences, CSJM University, Kanpur
  • 2. Basics of Radiation Measurements Radiation measurements are essential for quantifying radiation exposure, absorbed dose, and activity, providing crucial information for medical physics and radiology. Let's delve deeper into the units and their significance: Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 2
  • 3. Gray (Gy) • Definition: One gray is equivalent to the absorption of one joule of radiation energy per kilogram of matter. • Example: If a tissue absorbs 2 joules of radiation energy per kilogram, the absorbed dose would be 2 Gy. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 3
  • 4. Sievert (Sv) • Definition: Sievert is a unit used to measure the biological effects of ionizing radiation on human tissue. • Conversion: 1 Sv = 100 rem (roentgen equivalent in man). • Example: If an individual receives a dose of 0.1 Sv, it implies a significant risk of developing radiation-induced cancer. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 4
  • 5. Exposure Unit (Roentgen) • The Roentgen (R) is a unit of measurement for ionizing radiation exposure, particularly in air. It quantifies the amount of ionization produced by X-rays or gamma rays in a specific volume of air. The Roentgen is crucial in radiation dosimetry and radiological safety. Let’s discuss into the theory of the Roentgen unit along with examples: Definition of Roentgen (R): • The Roentgen is defined as the amount of X-ray or gamma radiation that produces one electrostatic unit of charge (either positive or negative) per cubic centimeter of air under standard conditions of temperature and pressure. • The symbol for the Roentgen unit is "R." Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 5
  • 6. Measurement of Radiation Exposure Radiation exposure is measured by instruments called ionization chambers, which detect the ionization of air molecules caused by incoming X-rays or gamma rays. When radiation interacts with air molecules, it liberates electrons, resulting in ion pairs (positive ions and free electrons). The ionization chamber measures the total charge produced by these ion pairs, which is directly proportional to the radiation exposure. Calculation and Examples: • One Roentgen (R) is equivalent to the generation of 2.58 × 10^−4 coulombs of charge per kilogram of air. • For example, if a certain X-ray beam produces an exposure of 100 R, it means that the radiation has caused the liberation of 2.58 × 10^−4 coulombs of charge per kilogram of air. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 6
  • 7. 4. Applications The Roentgen unit is commonly used in various applications, including: • Diagnostic radiology: To measure the intensity of X-ray beams used in medical imaging procedures such as radiography and fluoroscopy. • Radiation safety: To assess occupational and environmental exposure to ionizing radiation and ensure compliance with safety regulations. • Radiation therapy: To monitor and control the dose of radiation delivered to cancerous tissues during radiotherapy treatments. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 7
  • 8. Becquerel (Bq) • The SI unit of radioactivity is the becquerel (Bq), named after Henri Becquerel, the physicist who discovered radioactivity. The becquerel is defined as one disintegration or radioactive decay event per second. It quantifies the activity of a radioactive substance, representing the rate at which its unstable atomic nuclei undergo radioactive decay. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 8
  • 9. Measurement of Radioactivity 1 becquerel (Bq) = 1 disintegration/second • Radioactivity is typically measured using specialized instruments such as Geiger- Muller counters, scintillation detectors, or proportional counters. • These instruments detect the ionizing radiation emitted by radioactive decay and convert it into electrical signals or light pulses. • The number of disintegrations detected per unit time provides the activity of the radioactive substance in becquerels. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 9
  • 10. Applications of the Becquerel Unit 1. Nuclear Medicine: 1. In medical imaging and therapy, radioisotopes are used as tracers or therapeutic agents. 2. The activity of radiopharmaceuticals is measured in becquerels to ensure the proper dosage for diagnostic or therapeutic procedures. 2. Environmental Monitoring: 1. In environmental science, the concentration of radioactive isotopes in air, water, soil, and food samples is measured to assess radioactive contamination. 2. Monitoring stations use becquerels to quantify the levels of radioactivity in the environment and to ensure public safety. 3. Industrial Applications: 1. In nuclear power generation, industrial processes, and non-destructive testing, radioisotopes are used for various applications. 2. The activity of radioactive materials in industrial processes is measured in becquerels to ensure safety and regulatory compliance. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 10
  • 11. REM The REM (Roentgen Equivalent Man) is a unit of dose equivalent, used to quantify the biological effect of ionizing radiation on human tissue. It takes into account both the absorbed dose of radiation and the relative biological effectiveness (RBE) of the type of radiation. The REM unit is crucial in radiation protection, occupational safety, and assessing the health risks associated with exposure to ionizing radiation. • Definition of REM: • The REM unit represents the dose equivalent in terms of the biological effect of ionizing radiation on human tissue. • It is defined as the product of the absorbed dose (measured in gray or rad) and a quality factor (dimensionless), which accounts for the type of radiation and its relative biological effectiveness. • 1 REM is equivalent to 0.01 sievert (Sv). Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 11
  • 12. Calculation of REM The formula to calculate REM is: REM=Absorbed Dose (in rad or Gy)×Quality Factor (dimensionless) • The quality factor depends on the type of radiation and ranges from 1 for low linear energy transfer (LET) radiation (such as X-rays and gamma rays) to higher values for higher LET radiation (such as alpha particles and neutrons). Examples of Quality Factors: • X-rays, gamma rays, and beta particles: Quality factor = 1 • Alpha particles: Quality factor = 20 • Neutrons: Quality factor varies depending on energy and circumstances, ranging from 2 to 20 or higher Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 12
  • 13. Applications of REM 1. Radiation Protection: 1. The REM unit is used in radiation protection guidelines and regulations to establish dose limits for occupational exposure to ionizing radiation. 2. Occupational dose limits are typically expressed in units of millirem (mrem) or REM. 2. Medical Dosimetry: 1. In medical radiation therapy, the REM unit is used to assess the potential biological effects of therapeutic doses of ionizing radiation on healthy tissues and organs surrounding the targeted tumor. 3. Risk Assessment: 1. The REM unit plays a crucial role in assessing the health risks associated with radiation exposure and determining the appropriate safety measures and protective actions to mitigate those risks. 1 REM = 0.01 Sv (sievert) 1 millirem (mrem) = 0.001 REM Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 13
  • 14. Example A radiation source emits radiation with an intensity of 10 mGy per hour at a distance of 1 meter. Calculate the absorbed dose at this distance. Solution: • The absorbed dose (D) can be calculated using the formula: D= Intensity × Time Given: Intensity = 10 mGy/hour, Time = 1 hour • Substitute the values into the formula: D= 10mGy/hour × 1hour =10mGy Therefore, the absorbed dose at a distance of 1 meter is 10 milligray. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 14
  • 15. Quality Specification in Radiology • Quality specification in radiology encompasses various parameters that ensure optimal performance and safety. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 15
  • 16. Image Resolution • Definition: Image resolution refers to the clarity or sharpness of an image, determined by the number of pixels or lines per unit length. • Example: In digital radiography, a higher resolution image allows for better visualization of fine anatomical structures, aiding in accurate diagnosis. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 16
  • 17. Image Contrast • Definition: Image contrast is the difference in brightness or density between adjacent areas on an image. • Example: Contrast is crucial in distinguishing between different tissues or pathological conditions. For instance, in mammography, a high contrast image helps detect subtle abnormalities in breast tissue. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 17
  • 18. Image Noise • Definition: Image noise refers to random fluctuations in pixel values, resulting in a grainy or speckled appearance. • Example: Noise reduction techniques are essential in computed tomography (CT) to improve image quality. High noise levels can obscure important details and compromise diagnostic accuracy. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 18
  • 19. Dose Optimization Definition: Dose optimization aims to minimize radiation exposure to patients while maintaining diagnostic image quality. Example: Utilizing dose-reduction techniques such as automatic exposure control (AEC) in radiography ensures that patients receive the lowest possible dose without compromising image quality. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 19
  • 20. Compliance with Standards Definition: Compliance with regulatory standards such as IEC 61223-3- 5 ensures adherence to specific quality assurance protocols. Example: Regular quality control checks, calibration of equipment, and documentation of procedures are essential for compliance with standards, guaranteeing consistent and safe radiological practices. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 20
  • 21. Half-Value Thickness (HVT) Half-Value Thickness (HVT) is a fundamental concept in radiation physics, particularly in shielding design and radiation protection. Let's delve deeper into HVT with numerical examples: Definition: 1. HVT is the thickness of a material required to reduce the intensity of a radiation beam by half. 2. It varies with the type and energy of radiation and the material through which it passes. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 21
  • 22. 1. Radiation Attenuation: When a radiation beam passes through a material, it interacts with the atoms in the material, resulting in attenuation or reduction in its intensity. • Attenuation can occur through processes such as absorption, scattering, and transmission. 2. Half-Value Thickness (HVT): HVT is defined as the thickness of a material that reduces the intensity of a radiation beam to half of its original value. • It serves as a measure of the effectiveness of a shielding material in attenuating radiation. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 22
  • 23. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 23
  • 24. 3. Factors Affecting HVT The HVT of a material depends on several factors, including: • Type of radiation: Different types of radiation (e.g., gamma, X-ray, neutron) have varying penetration depths and require different thicknesses of shielding material. • Energy of radiation: Higher energy radiation typically requires thicker shielding for attenuation. • Atomic number (Z) and density of the material: Materials with higher atomic numbers and densities are more effective in attenuating radiation and may have smaller HVT values. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 24
  • 25. 4. Applications and Examples Medical Radiology: - In diagnostic radiology, lead aprons are commonly used to shield patients from scattered radiation during X-ray procedures. Example: The HVT of lead for diagnostic X-rays may range from a few millimeters to several centimeters, depending on the energy of the X- rays and the required level of attenuation. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 25
  • 26. Industrial Radiography: - In industrial radiography, lead or concrete shielding is used to protect workers from exposure to radiation during non-destructive testing. Example: The HVT of concrete for gamma radiation used in industrial radiography may be several centimeters, ensuring adequate protection for workers in the vicinity. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 26
  • 27. Nuclear Engineering: - In nuclear power plants, shielding materials such as steel and concrete are employed to minimize radiation exposure to personnel and the surrounding environment. Example: The HVT of steel for neutron radiation in nuclear reactors may be significant, requiring thick shielding to prevent radiation leakage. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 27
  • 28. 5. Measurement and Calculation • HVT can be determined experimentally by measuring the intensity of radiation before and after passing through various thicknesses of shielding material. • Calculation of HVT involves logarithmic functions and is based on the relationship between intensity and thickness of the shielding material. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 28
  • 29. Example Initial intensity of a gamma radiation beam: I0=100 mR/hourI0​=100mR/hour, HVT of lead for this radiation: HVT Lead = 0.5 cm HVT Lead​ = 0.5cm The formula to calculate the intensity after passing through a thickness of material is given by: I=I0×0.5n Where: I = Final intensity after passing through thickness n = Number of HVTs of the material In this case, we want to find the intensity after passing through 1 cm of lead (which is twice the HVT): n = ​​ Thickness of lead 𝐻𝑉𝑇 𝐿𝑒𝑎𝑑 = 1𝐶𝑚 0.5 𝑐𝑚 = 2 cm Substitute n = 2 into the formula: I =100mR/hour × 0.52 =100mR/hour×0.25 = 25mR/hour Interpretation: This means that after passing through 1 cm of lead, the intensity of the gamma radiation beam reduces to 25 mR/hour. Such calculations are vital for designing effective radiation shielding in medical facilities, ensuring the safety of patients and staff. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 29
  • 30. Filters in Radiology Filters play a crucial role in radiology by modifying the quality and energy spectrum of X-ray beams. Their function and selection is essential for achieving optimal image quality while minimizing patient dose. Let's explore this topic in detail, including common filter materials and their effects on the X-ray spectrum: Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 30
  • 31. Purpose of Filters • Filters are employed in radiology to alter the energy distribution of X- ray beams, thereby optimizing image quality and reducing patient dose. • By selectively filtering out low-energy photons, filters help enhance image contrast and reduce scattered radiation, resulting in clearer diagnostic images. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 31
  • 32. Common Filter Materials • Aluminum (Al): Aluminum filters are commonly used in X-ray equipment for general radiography. They effectively remove low-energy photons from the X-ray beam, improving image quality and reducing patient dose. • Copper (Cu): Copper filters are utilized in mammography to enhance the visualization of breast tissue. They selectively attenuate low-energy X-rays, allowing for better contrast and detection of subtle abnormalities. • Molybdenum (Mo): Molybdenum filters are specifically designed for mammography applications. They help optimize the energy spectrum of X-rays, improving the visibility of microcalcifications and small lesions in breast tissue. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 32
  • 33. Effects of Filters on X-ray Spectrum • Filters preferentially absorb lower-energy X-rays, resulting in a "hardening" of the X-ray spectrum. • As a result, the average energy of the X-ray beam increases, leading to greater penetration of tissues and improved contrast resolution. • Additionally, filters reduce the amount of low-energy radiation reaching the patient's skin, thereby lowering skin dose and minimizing radiation risks. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 33
  • 34. Importance of Filtration Filtration is a critical aspect of radiology that significantly influences image quality, patient safety, and radiation dose management. The importance of filtration is essential for radiographers, radiologists, and other healthcare professionals involved in diagnostic imaging. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 34
  • 35. Enhancement of Image Quality • Filtration helps improve image quality by selectively attenuating low- energy photons, which are more likely to be absorbed by the patient's body tissues and contribute to image noise. • By removing these low-energy photons, filtration reduces scatter radiation and enhances image contrast, allowing for better visualization of anatomical structures and pathological findings. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 35
  • 36. Reduction of Patient Dose • One of the primary objectives of filtration is to minimize patient radiation dose while maintaining diagnostic image quality. • By filtering out low-energy radiation that contributes minimally to image formation, filtration helps reduce unnecessary radiation exposure to the patient's skin and underlying tissues. • This is particularly important in pediatric imaging and for patients undergoing repeated X-ray examinations, where dose optimization is critical for long-term radiation safety. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 36
  • 37. Compliance with Regulatory Standards • Regulatory bodies such as the Food and Drug Administration (FDA) and the International Electrotechnical Commission (IEC) establish guidelines and standards for filtration requirements in diagnostic X-ray equipment. • Compliance with these standards ensures that imaging systems meet minimum filtration specifications, guaranteeing consistent and safe radiation output. • Regular quality control checks and documentation of filtration parameters are essential components of quality assurance programs in radiology departments. • Filtration plays a crucial role in reducing scatter radiation, which can degrade image quality and increase patient dose. • By attenuating low-energy photons that contribute to scatter, filters help improve the signal-to-noise ratio in X-ray images, resulting in clearer and diagnostically relevant images. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 37
  • 38. Types of Filtration • In radiology, various types of filtration are employed to tailor the energy spectrum of X-ray beams, optimize image quality, and minimize patient radiation dose. The different types of filtration and their applications is essential for radiographers, radiologists, and other healthcare professionals involved in diagnostic imaging. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 38
  • 39. Inherent Filtration Definition: Inherent filtration refers to the filtration that naturally occurs as X-rays pass through the components of the X-ray tube and the surrounding materials before reaching the patient. Components: Inherent filtration includes the glass envelope of the X-ray tube, the oil surrounding the X-ray tube, and any additional filtration within the X-ray tube housing. Purpose: The primary purpose of inherent filtration is to remove low-energy, soft X-rays generated by the X-ray tube, thereby ensuring that the X-ray beam has sufficient energy to penetrate the patient's body and produce diagnostic images. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 39
  • 40. Added Filtration Definition: Added filtration involves the placement of additional filters between the X-ray tube and the patient to further modify the energy spectrum of the X-ray beam. Materials: Common materials used for added filtration include aluminum, copper, and rare-earth metals such as gadolinium. Purpose: Added filtration helps attenuate low-energy X-rays that are not useful for diagnostic purposes and contribute primarily to patient dose and image noise. By removing these low-energy photons, added filtration enhances image quality and reduces radiation exposure to the patient. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 40
  • 41. Total Filtration Definition: Total filtration is the sum of inherent filtration and added filtration. Calculation: Total filtration is calculated by adding the filtration contributed by the components of the X-ray tube (inherent filtration) to the filtration provided by any additional filters (added filtration). Significance: Total filtration determines the overall quality of the X-ray beam in terms of its energy distribution and penetration characteristics. It is a crucial parameter for ensuring compliance with regulatory standards and optimizing radiation safety in diagnostic imaging. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 41
  • 42. Example: Where we have an X-ray machine with inherent filtration of 0.5 mm aluminum equivalent and an additional aluminum filter of 2.0 mm thickness placed between the X-ray tube and the patient. We want to calculate the total filtration provided by the X- ray machine. Inherent Filtration: Inherent filtration refers to the filtration naturally present within the X-ray tube. Given inherent filtration: 0.5 mm aluminum equivalent. Added Filtration: Added filtration consists of additional filters placed between the X-ray tube and the patient. Given added filtration: 2.0 mm aluminum. Total Filtration: Total filtration = Inherent filtration + Added filtration = 0.5 mm aluminum equivalent + 2.0 mm aluminum = 0.5 mm + 2.0 mm = 2.5 mm aluminum equivalent. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 42
  • 43. Compensating Filtration Definition: Compensating filtration involves the use of filters that vary in thickness across the X- ray beam to compensate for variations in tissue thickness and density within the patient's body. Applications: Compensating filters are commonly used in mammography and dental radiography to achieve uniform image density and contrast across the entire image, even in regions with varying tissue thicknesses. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 43
  • 44. References 1. Bushberg, J. T., Seibert, J. A., Leidholdt Jr, E. M., & Boone, J. M. (2011). The Essential Physics of Medical Imaging. Lippincott Williams & Wilkins. 2. Rehani, M. M., & Szczykutowicz, T. P. (Eds.). (2012). Radiation Dose Management in the Nuclear Industry: An Integrated Approach. Springer Science & Business Media. 3. The International Electrotechnical Commission. (2017). IEC 61223-3-5: Medical electrical equipment - Characteristics of digital X- ray imaging devices - Part 3-5: Determination of the detective quantum efficiency - Detectors used in mammography. IEC. 4. Shrader, J. A., Casarella, W. J., & Ritenour, E. R. (2016). Introduction to Health Physics. CRC Press. 5. Valentin, J. (2007). Radiation and Your Patient: A Guide for Medical Practitioners. International Atomic Energy Agency. Units of Radiation Measurements, Quality Specification, Half- Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar 44